Explosion proof box with door mounted switch

ABSTRACT

A rigid cast box has a rectangular flange encircling the box opening. A cover has a mating flange which is bolted to the box flange to define an explosion proof enclosure. The cover is also hinged to the box so that it will be supported when the bolts are removed. Attached to the inside of the cover is an electrical switch. A handle on the face of the cover is rotatable to actuate the switch. The cover also carries the socket of a mating plug and socket combination. An interlocking apparatus connects the socket and the switch handle so that the switch cannot be turned on without having the plug all the way in the socket and, when the switch is turned on, the plug cannot be removed from the socket.

llnited States Patent [191 Appleton et a1.

[451 May 22,1973

[54] EXPLOSION PROOF BOX WITH DOOR MOUNTED SWITCH [75] Inventors: Arthur I. Appleton, Northbrook; Duncan Turner, Des Plaines; Robert J. Pastorel, Chicago, all of I11.

[73] Assignees Appleton Electric Company,

Chicago, Ill.

[22} Filed: May 10, 1971 [21] Appl. No.: 141,670

[52] US. Cl. ..200/168 G, 200/50 B [51] Hint. Cl. ..II01h 9/04 [58] Field of Search ..200/168 G, 50 B [56] References Cited UNITED STATES PATENTS 3,350,532 10/1967 Appleton ..200/l68 G 2,015,543 9/1935 Bissell ..200/50 B 3,385,945 5/1968 Tums ..200/l68 G 2,886,675 5/1959 Berry ..200/l68 G 3,264,443 8/1966 Farina et a1 ....200/l68 G X FOREIGN PATENTS OR APPLICATIONS 1,140,064 1/ 1969 Great Britain ..200/ 168 G Primary Examiner-Robert K. Schaefer Assistant Examiner-William J. Smith Att0rney- Howard H. Darbo, Louis Robertson and Edward C. Vandenburgh [5 7 ABSTRACT A rigid cast box has a rectangular flangeencircling the box opening. A cover has a mating flange which is bolted to the box flange to define an explosion proof enclosure. The cover is also hinged to the box so that it will be' supported when the bolts are removed. Attached to the inside of the cover is an electrical switch. A handle on the face of the cover is rotatable to actuate the switch. The cover also carries the socket of a mating plug and socket combination. An interlocking apparatus connects the socket and the switch handle so that the switch cannot be turned on without having the plug all the way in the socket and, when the switch is turned on, the plug cannot be removed from the socket.

9 Claims, 6 Drawing Figures PATENTEW- R 3,735,078

SHEET 1 BF 2 N INVENTORS 7: 3 ARTHUR APPLETON 0 lg. ou/vcmv ruR/vER 37 ROBERT .1. PASTOREL 3 J BYMJ 65 rrys EXPLOSTON PROOF BOX WITH DOOR MOUNTED SWITCH SUMMARY OF THE INVENTION The present invention relates to an explosion proof box incorporating a switch, having features to facilitate the maintenance of the switch, and also having a plug and socket combination of a character to prevent accidental ignition of explosive atmospheres externally of the box.

DESCRIPTION OF THE DRAWINGS FIG. I is a front view of a box embodying the present invention;

FIG. 2 is an inside view of the box cover with the switch removed;

FIG. 3 is a partial section as viewed at line 33 of FIG. I; I

FIG. 4 is a view of the electrical socket as seen at line 44 of FIG. 3;

FIG. 5 is an enlarged partial section as viewed at line 55 of FIG. 4 with the plug withdrawn from the socket; and

FIG. 6 is a view corresponding to FIG. 5 but showing the plug inserted in the socket.

DESCRIPTION OF SPECIFIC EMBODIMENT The following disclosure is offered for public dissemination in return for the grant of a patent. Although it is detailed to ensure adequacy and aid understanding, this is not intended to prejudice that purpose of a patent which is to cover each new inventive concept therein no matter how others may later disguise it by variations in form or additions or further improvements. The claims at the end hereof are intended as the chief aid toward this purpose, as it is these that meet the requirement of pointing out the parts, improvements, or combinations in which the inventive concepts are found.

In the illustrated embodiment there is a box body, generally 10, having a cover, generally 11. The box body has an internal opening 12. At the front of this internal opening the box body has a rectangular, planar flange 13 surrounding the opening. The cover has a mating flange 14 which likewise defines the external end of an opening 15 within the cover. A plurality of bolts 16 extend through openings 17 in-the cover and are threaded into the box body. These pull the two flanges securely together. This plus the width of the flanges insures that should an explosion take place within the box it will be confined to the space within the box and no flame will pass to the outside of the box to ignite an explosive atmosphere externally of the box.

Two hinge parts 19 are secured to the box body 10 and are aligned with two hinge parts 20 secured to the cover 11. These hinge parts are connected by pins 21 so that the cover is supported by the box body and can be swung away from the body to an open position. The pin is affixed to one of the hinge parts (e.g. 19) and rotatable in the other hinge part (e.g. 20) so that, after the bolts have been removed, the cover can be lifted to separate the hinge parts and permit the cover to be moved to another location.

Within the cover are mounting brackets 23 secured to the cover by screws 24 and to a switch 25 by screws 26. Switch 25 could be any of a number of electrical switches of a conventional type. Suffice it to say that it has an actuating lever 27 which is moved in the manner of a toggle switch to provide an electrical connection or to break thatelectrical connection.

A shaft 29 is rotatably journaled in the cover and has a handle 30 attached to its external end so that it may be manually rotated. Secured to the inner end of the shaft is a lever 31 having one end affixed to the shaft and the other end is bifurcated so as to slideably fit in a groove 32 of a ring 33. The ring has a central opening sufficiently large to slip over switch lever 27. Thus, as the handle 30 is turned, the ring 33 moves up and down, as viewed in FIG. 2, to actuate the switch through the movement of lever 27. The ring can slide in the bifurcated end of the lever so as to adjust for the requirement for linear movement to transfer switch lever 27 from the switch-on to the switch-off position and vice versa. A spring 34 is in compression between the lever 31 and the inner wall of the cover 11.

The cover 11 has a generally downwardly facing wall 36 on which is mounted an electrical socket, generally 37. This socket has a sleeve 38 with an internal opening 39 of a size to receive a plug, generally 40. The details of the electrical connections made through the plug and socket are unimportant to the present invention. Suffice it to say that the plug has a cylindrical shell 41 of a size to fit easily into the opening 39. Shell 41 has a radial opening 42 therein. The plug and socket have conformations, not shown, so that the two must be rotationally aligned before the plug can be inserted into the socket. When the plug is all the way in the socket so that the electrical connections between the plug and socket are assured, opening 42 is aligned with a plunger 44. Plunger 44 is movable axially thereof in the casting or body 45 that forms the sleeve 38. The plunger has a handle 46 on its external end. It is urged inwardly by a spring 47 which is in compression between a part of the body 45 and a C washer 48 engaged in a groove on the plunger. Plunger 44 has two slots on a side thereof with the slots being normal to the axis of the plunger. One of these slots defines abutments 49 and 50. The other of the slots defines abutments 51 and 52.

A first reciprocating member 55 is mounted in body 45 for movement parallel to the longitudinal axis of the reciprocating member. This members axis is normal to the axis of plunger 44 but is offset to one side thereof. As viewed in FIGS. 5 and 6, the axis of member 55 is behind the axis of plunger 44. One side of reciprocating member 55 has been cut away to define a flat 56 with an abutment 57 at the end thereof. Normal to flat 56 is a slot in member 55 whichdefines abutments 58 and 59. A connecting rod 60 is pinned to one end of member 55 and to a central area of lever 31.

A second reciprocating member 63 is mounted in body 45 for longitudinal movement therein. This member has a portion cut away to define a flat 64 with an abutment 65 at the end of the flat. The longitudinal axis of member 63 is parallel to the longitudinal axis of member 55 and, like member 55, is behind the longitudinal axis of plunger 44. Normal to flat 64 is a slot which defines abutments 66 and 67. Intermediate the ends is an annular groove 68. A spring 69 is in compression between the body 45 and the right end of member 63 to urge that member to the left as viewed in FIGS. 5 and 6. Plugs 70 close the ends of the bores in body 45 in which the reciprocating members are positioned. A bifurcated feeler or actuator 73 extends into groove 68. It has one end bearing on body 45 and the other end extends into opening 39 to contact the plug 40 as the plug is moved into the socket.

In the usual event, the power supply wires will be brought into box through enclosed conduits, not shown. These wires can connect directly to switch 25 but, preferably, will connect to a terminal block 75 and rather long flexible pigtail leads 76 will provide an electrical connection to supply the power from the terminal block to the switch. From the switch, wires 77 make an electrical connection to the contacts of socket 37. When the switch 25 is in the closed or on position an electrical connection is made from the power supply to the socket and this electrical connection is broken when the switch is turned to the off" position.

The handle 30 is shown in the switch-off position in FIG. 1. This corresponds to the position of the reciprocating member 55 illustrated in FIG. 5. The part of plunger 44 between abutments'50 and 51 extends into the slot on member 55 between abutments 58 and 59. This prevents the member 55 from moving to the right in FIG. 5. The handle 30, therefore, is locked in the off" position and the switch 25 cannot be closed to supply electricity to socket 37. Abutment 51 of plunger 44 bears against that part of reciprocating member 63 which is just to the left of abutment 65 and to the right of abutment 67. This prevents the plunger 44 from moving inwardly in response to the urging of spring 47. Thus, the reciprocating member 55 and the plunger 44 are blocked in the respective positions illustrated in FIG. 5. Spring 69 holds the reciprocating member 63 in the FIG. 5 position.

When the plug 41 is moved into the socket 37 it ultimately contacts the end of actuator 73. This would not take place until after the electrical connections were established between the electrical members of the plug and socket, respectively. When the plug is fully seated in the socket (the FIG. 6 position), the opening 42 is aligned with the end of the plunger 44. Also, the actuator 73 has been pivoted about its opposite end so as to force reciprocating member 63 to the right and compress spring 69. The movement of the reciprocating member 63 to the right withdraws that portion of the member that had been in contact with abutment 51 of plunger 44; that is, when the plug is fully seated in the socket, the slot between abutments 66 and 67 of member 63 is aligned with abutment 51 so that abutment 51 no longer is in contact with member 63. This permits the plunger 44 to move inwardly in response to the urging of spring 47. With this inward movement the end of plunger 44 enters opening 42 to prevent the plug 41 from being withdrawn from the socket so long as the plunger is in the FIG. 6 position.

This movement of plunger 44 into locking engagement with the plug 41 results in freeing reciprocating member 55. Thus, that part of plunger 44 that exists between abutments 50 and 51 moves out of the path of movement of abutment 58 and is replaced by the slot between abutments 49 and 50. Since reciprocating member 55 now is free to move to the right from its FIG. 5 position, handle 30 can be rotated upwardly. This rotational movement pulls reciprocating member 55 upwardly as seen in FIG. 2, and to the right from the FIG. 5 to the FIG. 6 position. At the same time the ring 33 connection between lever 31 and switch lever 27 results in the actuation of the switch to the switch-on" position. This position of the interlocking apparatus is illustrated in FIG. 6. At this time, that portion of reciprocating member 55, which is to the left of abutment 58 in FIGS. 5 and 6, has moved into the path of movement of plunger 44. Thus, plunger 44 cannot be moved outwardly (up in FIGS. 5 and 6) so long as reciprocating member 55 is in the FIG. 6 position (corresponding to switch-on). Plunger 44 is now locking the plug 41 in the socket and cannot be unlocked because of the position of reciprocating member 55.

If the plug 41 is to be removed from its socket, the

reciprocating member 55 first must be returned from the FIG. 6 to the FIG. 5 position. This is done by rotating handle 30 down to the FIG. 1 position. Such manual rotation of the handle turns off the switch 25 and at the same time returns the reciprocating member 55 to the FIG. 5 position. Now the abutment 50 of plunger 44 no longer is blocked by member 55 since the slot between abutments 58 and 59 is aligned with the path of movement of abutment 56. The operator now can grasp handle 46 and pull the plunger 44 to the FIG. 5 position. While using one hand to hold the plunger 44 in the FIG. 5 position, the operator grasps the plug 41 with the other hand and removes it from its socket. This allows spring 6? to return reciprocating member 63 to the FIG. 5 position at which it now blocks the plunger 44 in the FIG. 5 position.

Thus, the plunger 44, the reciprocating members 55 and 63, the actuator 73, along with their associated parts, forms an interlock between the plug and socket and the switch to: (I) prevent the switch from being moved to the switch-on position until the plug 41 is fully seated in the socket 37 (thus making electrical connection therebetween) and (2) prevent the plug 41 from being removed from the socket 37 so long as the 'switch 25 is in the switch-on position.

An important feature of the described invention is the ability to readily service the switch 25. Apparatus of the present type is used for handling comparatively large power requirements. Switch 25 even could be a motor starter. In such applications arcing within the switch 25 will often pit the contacts and in time the switch will require servicing or replacement. When this occurs, the operator, after shutting down the power line elsewhere, removes the bolts 16 that hold the cover 11 in place on the box 10. This permits the cover to be swung outwardly toward the FIG. 2 position. The flexible leads 76 facilitate this operation. The leads 76 are disconnected from the switch. The operator now has two choices. He either can remove the switch 25 from the box or he can lift the cover from the box and take the cover and switch away for servicing at a location where suitable servicing equipment is readily available. The latter option is carried out merely by lifting the cover upwardly to release the connection provided by pins 21. If it is decided to leave the cover in place, the screws 24 can be withdrawn so as to detach the switch 25 from the cover. A new switch can be easily replaced by transferring brackets 23 to the new switch and moving the switch into place at which time the switch lever 27 is inserted into ring 33. The screws 24 then are replaced to hold the new switch in the box. As compared to prior art arrangements where the switch was mounted in the box, rather than the cover, there is a very significant advantage. The operations necessary to replace the switch are easily carried out when the switch is on the cover. When the switch was in the box 10 the space in which to work was extremely limited making it a difficult and time-consuming operation; thus, adding to servicing expense.

With the described apparatus, if an electrical arc is to occur it will occur within the enclosure defined by the box with the cover secured thereto. No particular effort is made to prevent an explosive mixture from getting into that enclosure and the opening of the switch contacts conceivably could cause an explosion therein. However, the strength of the box and the fact that the cover is securely tied thereto by the bolts 16 prevents any rupturing of the enclosure so that flame could escape. The large flat flanges on the box body and cover are an immediate juxtaposition and will cool any effort of a flame to pass between the flanges to an extent such that the flame cannot escape by that path. The electrical connections supplied by the connecting parts between the plug and socket cannot be made or broken so long as the switch 25 is in the switch-on position. They can only be made or broken when the switch is in the switch-off position. This prevents any arcing externally of the enclosure which arcing might otherwise ignite an explosive atmosphere about the box.

We claim:

1. An explosion proof switch apparatus comprising:

a box comprising a main body, a cover and means releasably connecting the body and the cover, said body and cover defining an internal chamber, said body and cover having mating flanges in immediate juxtaposition to each other and preventing the propagation of flame therebetween, said means including bolts releasably attaching the cover to the box;

an electrical switch removably mounted on and attached to the inside of said door;

switch operating means extending through said door, connected to said switch, and having a handle on the outside of said door for actuation of said switch;

said connecting means including a hinge supporting the cover from the box body, said hinge having a part on the box body and a part on the cover, said parts being readily separable so that the cover can be detached from the body.

2. An explosion proof switch apparatus comprising:

a box comprising a main body, a cover and means releasably connecting the body and the cover, said body and cover defining an internal chamber, said body and cover having mating flanges in immediate juxtaposition to each other and preventing the propagation of flame therebetween, said means including bolts releasably attaching the cover to the box;

an electrical switch removably mounted on and attached to the inside of said door;

switch operating means extending through said door, connected to said switch, and having a handle on the outside of said door for actuation of said switch;

an exposed power supply terminal block within the box body and affixed thereto, and flexible pigtail wires extending from said switch to said block.

3. An explosion proof switch apparatus comprising:

a box comprising a main body, a cover and means releasably connecting the body and the cover, said body and cover defining an internal chamber, said body and cover having mating flanges in immediate juxtaposition to each other and preventing the propagation of flame therebetween, said means including bolts releasably attaching the cover to the box; a

an electrical switch removably mounted on and attached to the inside of said door;

switch operating means extending through said door,

connected to said switch, and having a handle on the outside of said door for actuation of said switch; and said cover having a downwardly facing front wall portion an electrical plug and socket, said socket being mounted on said portion facing downwardly.

4. An explosion proof switch apparatus comprising:

a box comprising a main body, a cover and means releasably connecting the body and the cover, said body and cover defining an internal chamber, said body and cover having mating flanges in immediate juxtaposition to each other and preventing the propagation of flame therebetween, said means including bolts releasably attaching the cover to the box;

an electrical switch removably mounted on and attached to the inside of said door;

switch operating means extending through said door,

connected to said switch, and having a handle on the outside of said door for actuation of said switch; and

a mating electrical plug and socket, said socket being mounted on said cover and electrically connected to said switch;

said operating means including an interlocking means operably associated with said socket for preventing said switch being actuated from a first position at which said socket is deenergized to a second position to energize said socket until said plug is mated with said socket sufficiently to produce an electrical connection therebetween and for preventing said plug being removed from said socket when said switch is in the position to energize said socket.

5. An apparatus as set forth in claim 4, wherein said cover has a downwardly facing front wall portion, said socket being mounted on said portion facing downwardly.

6. An apparatus as set forth in claim 4, wherein said plug has a part which is received in the socket when the two are mated, said part having a side wall with an opening therein;

said interlocking means including a plunger mounted in the socket and aligned with said opening for movement normal to said wall between an effective position at which it extends into said opening and a retracted position at which it is spaced from said opening, and means operatively connecting said plunger and said switch to prevent said switch being moved from the first to the second position unless said plunger extends into said wall opening and prevents said plunger from being withdrawn from thewall opening unless the switch is in the first position.

7. An apparatus as set forth in claim 6, wherein said interlocking means includes a feeler moved from a first to a second position when said plug is inserted into said socket and from the second to the first position when the plug is withdrawn from the socket, a first reciprocating part movable along a line normal to said plunger and connected to said feeler to be moved thereby, a

second reciprocating part movable along a line normal to said plunger and connected to said handle, said first reciprocating part having an abutment blocking the movement of the plunger from the retracted to the effective position when the feeler is in the first position, said abutment being moved out of blocking position when the feeler is in the second position, said plunger having an abutment blocking the movement of the second reciprocating part when the plunger is in the retracted position, said plunger abutment being moved out of blocking position when the plunger is in the effective position, said second reciprocating part having an abutment blocking the movement of the plunger when the plunger is in the effective position and the switch is in the second position, said second part abutment being moved out of blocking position when the switch is in the first position.

8. An apparatus of the type described comprising:

an explosion proof switch box;

an electrical switch in said box movable from a first, switch-off position to a second, switch-on position and vice versa;

a mating plug and socket, said socket being mounted on said box, said plug having a part which is received in the socket when the two are mated, said part having a side wall with an opening therein; and

switch operating means including an interlocking means operably associated with said socket for preventing said switch being actuated from a first position at which said socket is deenergized to a second position to energize said socket until said plug is mated with said socket sufficiently to produce an electrical connection therebetween and for preventing said plug being removed from said socket when said switch is in the position to energize said socket, said interlocking means including a plunger mounted in the socket and aligned with said opening for movement normal to said wall between an effective position at which it extends into said opening and a retracted position at which it is spaced from said opening, and means operatively connecting said plunger and said switch to prevent said switch being moved from the first to the second position unless said plunger extends into said wall opening and prevents said plunger from being withdrawn from the wall opening unless the switch is in the first position.

9. An apparatus as set forth in claim 8, wherein said interlocking means includes a feeler moved from a first to a second position when said plug is inserted into said socket and from the second to a first position when the plug is withdrawn from the socket, a first reciprocating part movable along a line normal to said plunger and connected to said feeler to be moved thereby, a second reciprocating part movable along a line normal to said plunger and connected to said handle, said first reciprocating part having an abutment blocking the movement of the plunger from the retracted to the effective position when the feeler is in the first position, said abutment being moved out of blocking position when the feeler is in the second position, said plunger having an abutment blocking the movement of the second reciprocating part when the plunger is in the retracted position, said plunger abutment being moved out of blocking position when the plunger is in the effective position, said second reciprocating part having an abutment blocking the movement of the plunger when the plunger is in the effective position and the switch is in the second position, said second part abutment being moved out of blocking position when the switch is in the first position. 

1. An explosion proof switch apparatus comprising: a box comprising a main body, a cover and means releasably connecting the body and the cover, said body and cover defining an internal chamber, said body and cover having mating flanges in immediate juxtaposition to each other and preventing the propagation of flame therebetween, said means including bolts releasably attaching the cover to the box; an electrical switch removably mounted on and attached to the inside of said door; switch operating means extending through said door, connected to said switch, and having a handle on the outside of said door for actuation of said switch; said connecting means including a hinge supporting the cover from the box body, said hinge having a part on the box body and a part on the cover, said parts being readily separable so that the cover can be detached from the body.
 2. An explosion proof switch apparatus comprising: a box comprising a main body, a cover and means releasably connecting the body and the cover, said body and cover defining an internal chamber, said body and cover having mating flanges in immediate juxtaposition to each other and preventing the propagation of flame therebetween, said means including bolts releasably attaching the cover to the box; an electrical switch removably mounted on and attached to the inside of said door; switch operating means extending through said door, connected to said switch, and having a handle on the outside of said door for actuation of said switch; an exposed power supply terminal block within the box body and affixed thereto, and flexible pigtail wires extending from said switch to said block.
 3. An explosion proof switch apparatus comprising: a box comprising a main body, a cover and means releasably connecting the body and the cover, said body and cover defining an internal chamber, said body and cover having mating flanges in immediate juxtaposition to each other and preventing the propagation of flame therebetween, said means including bolts releasably attaching the cover to the box; an electrical switch removably mounted on and attached to the inside of said door; switch operating means extending through said door, connected to said switch, and having a handle on the outside of said door for actuation of said switch; and said cover having a downwardly facing front wall portion an electrical plug and socket, said socket being mounted on said portion facing downwardly.
 4. An explosion proof switch apparatus comprising: a box comprising a main body, a cover and means releasably connecting the body and the cover, said body and cover defining an internal chamber, said body and cover having mating flanges in immediate juxtaposition to each other and preventing the propagation of flame therebetween, said means including bolts releasably attaching the cover to the box; an electrical switch removably mounted on and attached to the inside of said door; switch operating means extending through said door, connected to said switch, and having a handle on the outside of said door for actuation of said switch; and a mating electrical plug and socket, said socket being mounted on said cover and electrically connected to said switch; said operating means including an interlocking means operably associated with said socket for preventing said switch being actuated from a first position at which said socket is deenergized to a second position to energize said socket until said plug is mated with said socket sufficiently to proDuce an electrical connection therebetween and for preventing said plug being removed from said socket when said switch is in the position to energize said socket.
 5. An apparatus as set forth in claim 4, wherein said cover has a downwardly facing front wall portion, said socket being mounted on said portion facing downwardly.
 6. An apparatus as set forth in claim 4, wherein said plug has a part which is received in the socket when the two are mated, said part having a side wall with an opening therein; said interlocking means including a plunger mounted in the socket and aligned with said opening for movement normal to said wall between an effective position at which it extends into said opening and a retracted position at which it is spaced from said opening, and means operatively connecting said plunger and said switch to prevent said switch being moved from the first to the second position unless said plunger extends into said wall opening and prevents said plunger from being withdrawn from the wall opening unless the switch is in the first position.
 7. An apparatus as set forth in claim 6, wherein said interlocking means includes a feeler moved from a first to a second position when said plug is inserted into said socket and from the second to the first position when the plug is withdrawn from the socket, a first reciprocating part movable along a line normal to said plunger and connected to said feeler to be moved thereby, a second reciprocating part movable along a line normal to said plunger and connected to said handle, said first reciprocating part having an abutment blocking the movement of the plunger from the retracted to the effective position when the feeler is in the first position, said abutment being moved out of blocking position when the feeler is in the second position, said plunger having an abutment blocking the movement of the second reciprocating part when the plunger is in the retracted position, said plunger abutment being moved out of blocking position when the plunger is in the effective position, said second reciprocating part having an abutment blocking the movement of the plunger when the plunger is in the effective position and the switch is in the second position, said second part abutment being moved out of blocking position when the switch is in the first position.
 8. An apparatus of the type described comprising: an explosion proof switch box; an electrical switch in said box movable from a first, switch-off position to a second, switch-on position and vice versa; a mating plug and socket, said socket being mounted on said box, said plug having a part which is received in the socket when the two are mated, said part having a side wall with an opening therein; and switch operating means including an interlocking means operably associated with said socket for preventing said switch being actuated from a first position at which said socket is deenergized to a second position to energize said socket until said plug is mated with said socket sufficiently to produce an electrical connection therebetween and for preventing said plug being removed from said socket when said switch is in the position to energize said socket, said interlocking means including a plunger mounted in the socket and aligned with said opening for movement normal to said wall between an effective position at which it extends into said opening and a retracted position at which it is spaced from said opening, and means operatively connecting said plunger and said switch to prevent said switch being moved from the first to the second position unless said plunger extends into said wall opening and prevents said plunger from being withdrawn from the wall opening unless the switch is in the first position.
 9. An apparatus as set forth in claim 8, wherein said interlocking means includes a feeler moved from a first to a second position when said plug is inserted into said socket and from the second to a first position when the plug is withDrawn from the socket, a first reciprocating part movable along a line normal to said plunger and connected to said feeler to be moved thereby, a second reciprocating part movable along a line normal to said plunger and connected to said handle, said first reciprocating part having an abutment blocking the movement of the plunger from the retracted to the effective position when the feeler is in the first position, said abutment being moved out of blocking position when the feeler is in the second position, said plunger having an abutment blocking the movement of the second reciprocating part when the plunger is in the retracted position, said plunger abutment being moved out of blocking position when the plunger is in the effective position, said second reciprocating part having an abutment blocking the movement of the plunger when the plunger is in the effective position and the switch is in the second position, said second part abutment being moved out of blocking position when the switch is in the first position. 